Electron multiplier



May Z7, 1941. G. wElss ELECTRON MULTIPLIER Original Filed Jan. 4, 1936 2 Sheets-Sheet l INVENTOR. f iff/5J' ATTORNEY.

May 27, 1941.

' EL-EcTRoN MULTIPLIER G. WEISS y 2,243,178

Origix-lal Filed Jan. 4. 1936 I 2 Sheets-Sheet 2 ATTORNY.

Patented May 27, 1941 ELECTRQN MULTRLIER Georg Weiss, Berlin, Germany Qriginal application January 4, 1936, Serial No.

Divided and this application June 4,

1938, Serial No. 211,730. In Germany `anuary 9 Ciaims.

This application is a division of my application Serial No. 57,584, filed January 4, 1936, and relates to electronic discharge apparatus. Its broad purpose is to provide a means of amplifying the intensity of an electron stream.

Among the objects of the invention are:

To provide a device for multiplying in stages the electrons available in electron discharge devices, photoelectric tubes and similar devices;

To subject the electron stream to a repeated amplification so that the number of electrons is increased from stage to stage;

To provide means by which a number of primary electrons is directed onto an anode emitting a large number of secondary electrons, to direct these secondary electrons onto a further anode to produce a still larger number of tertiary electrons and so forth.

The invention has numerous other objects and features, some of which will be set forth in the following description. It is to be understood that the invention is not limited to this disclosure as Variant embodiments thereof may be adopted within the scope of the claims.

It is known that primary electrons hitting an anode are adapted to liberate secondary electrons. Each primary electron having a certain velocity and hitting the anode may liberate a plurality of secondary electrons which can be collected by an auxiliary electrode for instance a grid. It

is known that the output of secondary electrons is particularly large when the primary electrons have a small angle of incidence, as it is the case for instance when they hit a screen consisting of thin wires. Also the material and the surface of the anode has an influence upon the number of liberated secondary electrons.

A device of this type is operated in the following manner: The primary electrons emitted by a cathode which may be incandescent or photoemissive are accelerated towards a first anode, and hit this anode. By impact of the primary electrons a number of secondary electrons are liberated, larger in number than the primary electrons. The anode is preferably made of silver having a very thin coating of an alkali metal, such as caesium or potassium, in order to facilitate the liberation of secondary electrons. Ii the anode has the form of a grid, a part of the primary electrons will hit the sides of the wires or that part of the surface of the screen wires having a large angle of inclination with respect to the plane of the screen. These electrons are particularly useful in producing secondary electrons.

(Cl. Z-41.5)

The secondary electrons are again accelerated in the direction of a following anode, having a higher potential, and a position close behind the rst anode. The secondary electrons impacting upon the second anode liberate a multiple number of tertiary electrons which are again accelerated in the direction of its following anode, and so on until iinally the collecting anode having a higher potential than the secondary emissive anodes'is reached. It is theoretically possible to in this vmanner obtain an amplification or multiplication of any desired degree.

The amplification of the changes of the primary current, which may be under the control of any suitable controlling influence, takes place with absolute proportionality. Experiments have shown that with a tube having a photoelectric cathode an amplification factor of 50 can be easily obtained with a primary noise level of only 0.1 microvolt. With such a tube it is possible Ato reduce the photo-tube resistance which is usually of the order of 5000 ohms, to only about 500 ohms. This is an advantage of great importance, for instance in the field of television and sound recording. But similar advantages are obtained in the distortionless amplification of broad frequency bands and in other uses of the device.

According to the present invention the anodes are so positioned and connected with such potentials, that a great number of secondary electrons run through the multiplying device twice. In this manner, a better eiciency is reached.

Referring to the drawings:

Fig. 1 is a schematic diagram of a device embodying a form of the invention, showing the principal circuit associated therewith.

Figs. 2, 3 and 4 show cross-sectional and partial views of specific embodiments.

Fig. 5 is a representation of an arrangement in which the paths of the electrons are indicated.

Figs. 6 and 7 show another modification, in schematic cross-section.

' Fig. 8 is a cross-section through a preferred form of a phototube, in combination with a device according to the invention.

Fig. 1 shows a plurality of grids of close mesh, or of metal foils lill and lll. Cathode 2 is in form of a photoelectric cathode. It is advantageous to arrange a collecting electrode I on the side of the row of anodes liil, lll directed towards the `cathode 2. It is possible in this way to force the electrons through the grids twice, so that the secondary emission is greatly increased. The last anode 3 consists in this case of a plate, through .which .the electrons :cannot pass. The anodes are maintained at successively decreasing potentials with the lowest potential on the anode, most remote from the cathode and with the highest potential on the collecting anode. The collecting anode is connected to the positive terminal of source of potential |I by way of an output resistance IB.

Fig. 2 shows an arrangement in which the anodes have the form of a ring in order not to obstruct the passage of light to the cathode. Another way of producing a similar effect is represented in Fig. 3, in which the grids consist of strips arranged on both sides of an elongated cathode surface. A further construction includes, according to Fig. 4 only .one set of secondary emission anodes consisting of narrow strips. The light falls upon the cathode on both sides of the strip-like anode structure, It is also preferable to heat the anode in order to decrease the energy for the liberation of the electrons.

Fig. 5 shows another Way of producing a stagewse increasing number of electrons. The anodes from which the secondary electrons are emit-ted consist of metal surfaces having -an inclined position.

v The primary electrons are accelerated by an acceleration-grid 4 and hit the anode 5 producing a multiplied number of secondary electrons. These electrons are again accelerated and directed towards the electrode |05. They liberate a multiplied number of tertiary electrons and so on. The figure shows two further anodes ||5 and and the collecting anode 3 connected to the output. Each of the anodes |05, ||5 and |25 is associated with a grid (|04, |l4, |24).

A further embodiment is represented in Figs. 6 and 7. In order to obtain a good result, it is preferable to form an electron-image of the source of electrons, for instance of a photoelectric cathode of a photoelectric tube or of an aperture situated in the stream of primary electrons, in the plane of the rst anode. It may also be of advantage to concentrate the complete stream of electrons emitted by the source 0f electrons upon the rst anode. Since the secondary electrons emitted by the first anode are flowing in dierent directions it is preferable to produce anelectron image of the rst anode in the plane of the second anode and an image of the second anode in the plane of the third anode and so on until an image of the last anode |3| is produced on the collecting anode 3. This can be accomplished in case a number of grids lying one behind the other is used by means of electrostatic lenses or by means of a magnetic field of a coil 6 surrounding the tube (Fig. '7). The electron lense may have the form of a cylinder and this has the advantage that if the arrangement is combined with a phototube, the phototube is shielded from outer influences. This is particularly of importance, when the tube is used for the purposes of television or sound-film. The cylinder is preferably connected with the shielding device ofthe input cable of the amplier, so that no other shielding devices as for instance metal boxes, metal grids and so on, are necessary and the light eiciency is increased.

Fig. 8 shows la form of construction which is of special advantage when a large cathode-.surface is desired. The tube has the form of a bulb 9, consisting of glass, and has aneck-portion 8 containing the electrode system |0|, |2|.

I claim:

1. An electron multiplying system including a cathode source of a primary electron stream of controllable intensity, a 4secondary emission anode in the path of said stream, a collecting anode having a surface portion capable of releasing secondary electrons upon electron impacting in a ratio greater than unity positioned between said cathode and said secondary emission anode, a source of potential, and means including circuit connections from said source of potential for maintaining said secondary electron emissive collecting anode at a potential higher than the potential of said secondary emission anode.

2. An electron multiplying system including a cathode source of a primary electron stream of controllable intensity, a secondary emission anode having a surface portion in the path of said stream capable of releasing secondary electrons upon primary electron impacting in a ratio greater than unity, a p erforate collecting anode having a surface portion capable of releasing secondary electrons upon electron impacting in a ratio greater than unity positioned between said cathode and said secondary emission anode, a source of potential, and means including circuit connections from said source of potential for maintaining said secondary electron emissive collecting anode at a potential higher than the potential rof said secondary emission anode.

3.v An electron multiplying system having a device including a cathode source of a primary electron stream of controllable intensity, a plurality of secondary emission anodes each having a surface portion capable of releasing secondary electrons upon electron impacting in a ratio greater than unity spaced from said cathode and maintained at successively decreasing potentials with the lowest potential on the anode most remote from said cathode, and a collecting anode positioned between said cathode and the most remote of said plurality of secondary emission anodes and maintained at a potential higher than the potentials of said secondary emission anodes.

4. An electron multiplying system having la device including a cathode source of a primary electron stream of controllable intensity, a collecting anode maintained at a predetermined potential with respect thereto, and a plurality of secondary emission anodes each having a surface portion capable of releasing secondary electrons upon electron impacting in a ratio greater than unity adjacent said collecting anode and remote from said cathode and maintained at potentials decreasing with increasing distance from said cathode.

5. An electron multiplying'system having a device including a cathode source of a primary electron stream of controllable intensity, and a plurality of anodes each having a surface portion in the path of said stream capable of releasing secondary electrons upon primary electron impacting in a ratio greater than unity each spaced at a successively increased distance from said cathode and maintained at potentials Varying according to their respective distances from said cathode with the least potential on the remote anode.

6. An electron multiplying system having a device including a Acathode source of a primary electron stream of controllable intensity, a foraminous collecting anode, a foraminous secondary emission anode remote from said cathode and adjacent said collecting anode, and an imperforate secondary emission anode remote from said collecting anode and adjacent said foraininous secondary emission anode, each of said secondary emission anodes having a surface portion capable of releasing secondary electrons upon electron impacting in a ratio greater than unity, said anodes being maintained at potentials decreasing successively with increase of distance from said Cathode.

7. An electron multiplying system having a device including a cathode source of a primary electron stream of controllable intensity, a plurality of secondary emission anodes each having a surface portion capable of releasing secondary electrons upon electron impacting in a ratio greater than unity disposed at successively increased distances froin said cathode and maintained at potentials decreasing with increase of distance from said cathode, a collecting anode positioned between said cathode and the most remote of said secondary emission anodes and having a potential higher than that of any of said secondary emission anodes, and output means in circuit connection between said collecting anode and said cathode.

8. An electron multiplying system including a photo sensitive cathode, a plurality of perforate secondary emission anodes spaced at successively increased distances from said cathode, a plateshaped secondary emission anode most remote from said cathode, each of said secondary emission anodes having a surface portion capable of releasing secondary electrons upon electron impacting in a ratio greater than unity, a perforate collecting anode positioned between the cathode and one of the secondary emission anodes and means for maintaining said collecting anode at a potential higher than the potential of the secondary emission anodes.

9. An electron multiplying system including a cathode source of a primary electron stream of controllable intensity, an imperforate secondary emission anode remote from said cathode having a surface portion in the path of said stream capable of releasing secondary electrons upon primary electron impacting in a ratio vgreater than unity, a collecting anode positioned between said cathode and said secondary emission anode, a plurality of perforate secondary emission anodes in the path of the electrons moving from said cathode towards said imperforate secondary anode each having a surface portion capable of releasing secondary electrons upon electron impacting in a ratio greater than unity, a source of potential, and means including circuit connections for said source for maintaining said collecting anode at a potential higher than the potential of said secondary emission anodes.

GEORG WEISS. 

